First off, congratulations, as a blended family you are a part of the largest grouping of families around! And yes, it is HARD! I'm a custodial stepmom (have been for 12 years) to my husband's 14 year old daughter and we have two boys together ages 9 and 3. Her biological mom hates me as well and through the years has aggressively tried to destroy the relationship I have built with her. It is a very hurtful thing and I've shed many tears, but this I know: I have given my daughter the freedom to love all her parents as she has 2 biological and 2 step. Her mom doesn't give her that freedom and that's what causes the conflict within and that's what counseling is for! I can only do what I can do. Love her unconditionally. Be there for her always. Speak her love language. Treat her with respect. I stay out of the conflicts between her bio parents - in fact it's a kind of bond we share that whatever goes on between her parents affects both of us whether we like it or not, so we girls gotta stick together. Prayer is my go to because I'm not in any sort of control, but I believe God put us together in a family for a reason. Routines are good. Conversations outside the house are good. Anything predictable is good.
I'm here if you need,